Preliminary prediction and evaluation of oligocene source rocks in Ledong-lingshui Sag in deep-water area of Qiongdongnan Basin
WANG Zisong;LIU Zhen;SUN Zhipeng;YAO Zhe;LIU Peng;CHEN Yuhang;WANG Bing;CHEN Jie;State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum;College of Geosciences, China University of Petroleum;Zhanjiang Brand of CNOOC Ltd.;
Whether source rocks are exist or not is the principal question which should be answered in the preliminary evaluation on the low-exploration area in the deep-water area and the importance of studying source rocks is obvious in the preliminary evaluation on the low-exploration area. Analysis of sequence stratigraphy and system tract, prediction of seismic velocity and lithology, associated prediction of vitrinite reflectance based on seismic and well-log data and the basin modeling technique, transformation from seismic facies and sedimentary facies to organic facies were used in turn on the basis of well data from the adjacent homologous sag and the geological comparison principle by comprehensively using the seismic, well-log and geochemistry data to predict the favored members, the thickness, the maturity and the maturation history, the distribution of organic facies and the quantity of Oligocene transitional and marine source rocks.At last, the source rocks were synthetically evaluated by calculating hydrocarbon-generation amount. The results shows that the most favored members of Oligocene source rocks are Ya-2 member and Ling-2 member during the six members; The thickness of two series of source rocks is large, and the maturation is high, but the hydrocarbon generation peak is a little late, so the late gas generation is a character of source rocks; The shallow-sea organic facies has large range and good quantity, so it is the most favored during the five organic facies, and the shallow-sea mud is the main source; Both of the source rocks have good quantity, and they are the most favored source rocks in the area, but comparatively, the quantity of source rocks in Ledong sag is better than Lingshui sag, and the hydrocarbon-generation amount of Ya-2 member is bigger than Ling-2 member. The evaluation system overcomes the difficulty which the rare data bring to, and is fit to the low-exploration deep-water area. So, it provides a resolve for the preliminary prediction and evaluation on source rocks in the low-exploration area.